The present invention relates to a heat transfer apparatus which is suited to the boiling cooling of high heat generating density members such as integrated circuits for electronic computers, power semiconductor devices including thyristors, and superconducting coils.
As a conventional method for promoting the boiling cooling of integrated circuit chips, there is the invention disclosed in U.S. Pat. No. 3,706,127. In this method, the chips are carried on a distributing board through solder bonding, and the surfaces of the chips are formed with a large number of metal whiskers (dendrites) by a metallurgical process. The aggregate of dendrites contains a large number of bubbling nuclei which are necessary for operating at a high temperature due to the heat generation of the integrated circuit chips and for generating the vapor bubbles of a dielectric liquid when the integrated circuit chips are immersed and operated in the dielectric liquid. Therefore, the heat generated by the integrated circuit chips can be promptly removed, and the temperature rise of the chips is suppressed even when large amounts of heat have been generated by the high speed operations of the electronic circuits built in the chips. With this method, however, such parameters as the growth interval and height of the dendrites and the size of voids included in the dendrite aggregate which function as the bubbling nuclei are governed by the process of dendrite growth. Since, in general, a surface structure produced by such metallurgical method is very fine, it is greatly effective for a low heat load. In contrast, when the heat flux of a heat generating surface increases, the generation of vapor becomes too active, and the surface is covered with a vapor film. As a result, the so-called burnout phenomenon in which the temperature of the surface rises suddenly is liable to occur. That is, the burnout heat flux is low, which leads to the disadvantage that the operating speed of a semiconductor device cannot be further increased because it has a limit value ascribable to the permissible quantity of heat generation which in turn is determined by the burnout heat flux.
Another method has been known wherein, as exemplified by U.S. Pat. No. 4,203,129, heat generating elements are furnished with a plate member having tunnel-like penetrant cavities and are immersed in a liquid coolant. In this example, the liquid is imbibed from below by a pumping action which occurs with the separation of bubbles from upper holes. Therefore, even when the quantity of heat generation is considerably large, the whole heat transfer surface is not covered with a vapor film, so that the burnout heat load is enhanced. With this method, however, almost no place for trapping vapor exists in the cavities, so that disadvantageously the performance is inferior at a low heat load.